The present invention is directed to articles and methods for permanently marking substrates.
With the advent of highly sophisticated and correspondingly complex electrical and electronic systems, a need has arisen for the detailed labeling of the individual wires and cables present in such systems to aid in the assembly, repair and/or subsequent alteration of the electrical or electronic device. As a result of this need, flexible, heat recoverable, polymeric marker sleeves have been developed which are either color coded or include printed indicia for identification of a specific wire. These sleeves are then positioned over the conductor and held by a variety of methods. The sleeves are then heated to recover them onto the conductor so that the conductor is permanently marked.
A variety of methods are available for printing indicia on these sleeves. One such method is transfer ribbon marking where transfer ribbons deposit ink on the surface of the sleeve such as with a typewriter. The ink must be cured or "permatized" on the sleeve to effect a permanent mark. Curing can be effected using infrared to obtain temperatures in the order of 600.degree. to 900.degree. F. for about one second.
A disadvantage of transfer ribbon marking is that during the heating step, the heat-recoverable sleeves can recover to their heat-stable position. To prevent this from occurring, the unmarked sleeves are loaded onto fingers or holders extending from a continuous carrier belt such as described in U.S. Pat. Nos. 3,894,731 and 4,032,010. However, the carrier belt, and the steps of loading and unloading the sleeves from the belt significantly increase the cost of marking.
Another marking method utilizes hot-stamp foils where heat and pressure are used to transfer ink from the foil onto the sleeve. This method is very time consuming and the hot-stamp foils have a limited shelf life if not properly stored. Further, it is difficult to obtain a high-quality permanent mark with hot-stamp foils because the quality of the mark is very sensitive to heat, pressure and time during the marking operation.
A third method for marking recoverable polymeric sleeves utilizes a specially formulated ink provided as an ink jet onto the surface of the sleeve. However, the ink used has a limited shelf life and the inking system is expensive. Furthermore, the marks produced with these inks have only limited solvent and abrasion resistance.
In view of these problems with conventional marking methods, it is apparent that there is a need for a system for permanently, economically, and reproducibly marking heat-recoverable, polymeric sleeves.